1. Field of the Invention
This invention relates to a plane light source unit and a radiant heating furnace including same. More particularly, this invention relates to a plane light source unit comprising a plurality of lamps disposed closely with each other in proximity to a mirror with the longitudinal axes of the lamps extending parallelly in a plane and a radiant heating furnace including the above plane light source unit and a cooling system therefor.
2. Description of the Prior Art
Among a variety of apparatus adapted to carry out heat treatments therein, radiant heating furnaces in which light radiated from a lamp or lamps irradiates objects or materials to be treated for heat treatment have the following merits:
(1) Owing to an extremely small heat capacity of a lamp per se, it is possible to raise or lower the heating temperature promptly;
(2) The heating temperature can be easily controlled by controlling the electric power to be fed to the lamp;
(3) Since they feature indirect heating by virtue of light radiated from their lamps which do not come into contact with the objects, there is little danger of contaminating objects under heat treatment;
(4) They enjoy less energy consumption because full-radiation-state operations of the lamps are feasible a short time after turning the lamps on and the energy efficiencies of the lamps are high; and
(5) They are relatively small in size and inexpensive compared with conventional resistive furnaces and high-frequency heating furnaces.
Such radiant heating furnaces have been used for the heat treatment and drying of steel materials and the like and the molding of plastics as well as in thermal characteristics testing apparatus and the like. Use of radiant heating furnaces have, particularly recently, been contemplated to replace the conventionally-employed resistive furnaces and high-frequency heating furnaces for heat treating of semiconductor wafers, such as, for example, drive-in diffusion processes, chemical vapor deposition processes, annealing processes of ion-implanted dopants and thermal processes for nitrifying or oxidizing the surfaces of silicon wafers. As reasons for the above move, using a radiant heating furnace, it is possible to activate the ion-implanted atoms with minimal redistribution because heat treating of the wafers at a higher temperature can be achieved in a shorter period of time, in addition to the advantages, such as little contamination, less power consumption, etc. Minimal redistribution of dopant implanted results in steeper and shallower junctions meaning potentially smaller and faster devices. Another reason is that with increasing semiconductor wafer size uniform heat treating by conventional resistive furnaces is more difficult.
As aforementioned, radiant heating furnaces have various merits and advantages and have already found wide-spread commercial utility in the industry. However, conventional radiant heating furnaces are accompanied by such drawbacks that they are unable to irradiate light onto objects of large areas and to heat them uniformly to high temperatures in short periods of time. In other words, each lamp is equipped with a sealed body made of silica glass or the like and forms a point or line light source. Thus, it is very difficult to form a plane light source having a two-dimensional extent when used solely. Accordingly, it cannot uniformly heat any region of a large area to a high temperature in a short period of time.